1. Field of the Invention
The present invention relates in general to plastic tubing and, more particularly, to apparatus and methods for making such tubing which is flexible and includes an external helical rib or bead.
2. Related Technology
Tubing which is flexible, and has a relatively thin wall and an integral helical supporting bead is known in the art. Such a flexible support-bead tubing construction provides substantial crush resistance while leaving the tube wall flexible enough to permit short-radius bends without collapsing or kinking the tube. The versatility of this kind of tubing is evidenced by its wide applicability in construction, ventilation, manufacturing processes, auto washes, medical devices, hospitals and other fields.
The walls of a support-bead tubing can be quite thin to minimize overall weight. This light weight for the tubing is an important feature when, for example, the tubing is used with an inhalation machine to provide a patient with more comfort during oxygen or medicated air delivery. Two other features of known thin wall support-bead or bead-reinforced tubing are transparency and smoothness of bore. Transparent plastic material permits inspection of the fluid coursing through the tube, to detect, for example, the presence of moisture in an anesthetic or patient oxygen delivery application. A smooth inner surface of such a tube is desirable to keep the tube free from deposits of contaminants and to discourage non-laminar flow. Also, this smooth inner surface makes the tubing product more desirable for applications in which the tubing is to be re-used. The smooth inner surface promotes easy and effective cleaning, sanitizing, and sterilizing of the tubing product.
U.S. Pat. No. 3,910,808 to Steward, discloses apparatus for forming a thin-walled, flexible, crush resistant tubing having a support-bead. Steward discloses a method for extruding a plastic strip having a longitudinal rib, and the method and apparatus for helically winding the strip about an axis to produce a corrugated flexible tubing having a smooth bore and a helical external support bead.
Many applications, however, require or are enhanced by the presence of controlled heating of such tubing. Neonatal patients, for example, as well as patients in shock or who are sustained on breathing equipment, are among those who benefit from gas flowing through heat-conditioned tubing.
U.S. Pat. No. 5,454,061 to Lenart Carlson, provides a helically wound and helically ribbed plastic tubing incorporating an electrically conductive heating wire and an apparatus and method for making the tubing. In this patent a plastic ribbon is wound about an axis into a tube with one edge of each lap overlapping and heat bonded to an edge of the preceding lap as the tubing is rotationally formed. A conductive wire is embedded in the ribbon and a bead is applied and heat-bonded onto the tubing, encapsulating the conductive wire during rotation of the tubing, and providing a unitary structure including a conductive wire integral to a flexible tubing. Again, the tubing has a corrugated crevice-free outside surface and a smooth inside surface. Coolant is applied to the tubing for cooling the unitary ribbon, wire, and bead during formation of the tubing, and also to assist in advancing the tubing along the axis of the manufacturing apparatus.
One prior application of a hollow ribbed pipe can be found in U.S. Pat. No. 5,051,081 assigned to Toyox. In this patent hollow ribs are produced by extrusion, and are then wrapped around the outer periphery of an extruded pipe. This construction of a tubing product has several deficiencies. For example, the interior walls of the hollow rib produced by this apparatus contain connection lines through which a gaseous material could escape into the ambient, and the rib is extruded in such fashion that it would not be possible to separate it from the tube and attach it to a hose barb. That is, the shape of the lumen or passage in this rib is not generally round.
A new application for such flexible tubing requires that a second lumen or passage be available for communication between the ends of the tubing. A preferred way of providing this second lumen or passage is to provide a lumen or passage inside and integrally defined by the support bead.
No prior product, method of manufacture, or apparatus is known which provides a transparent, sterilizable, thin-walled, smooth bore tube having a contemporaneously wound supporting and encapsulating bead defining a lumen, or defining plural lumens, each suitable for communicating a fluid between the ends of the tubing product, and with the bead, and tube forming a unitary structure with a smooth, crevice-free outer surface.
In view of the deficiencies of the related art as discussed above, it is a primary object of the present invention to provide a flexible, lightweight, crush-resistant tubing having one or plural supporting bead helically wound about and integral with the surface of the tubing. The is constructed with smooth walls free from joints or connection lines. The bead defines one lumen or plural lumens capable of transporting or communicating a fluid or gas without leakage to the ambient.
It is another object of this invention to provide apparatus and method for inexpensively making a tubing product, supporting bead with at least one interior lumen, and tube wall as a unitary body free of adhesive and binders and having a smoothly corrugated outer surface free of crevices.
Yet another object for this invention is to provide a method and apparatus for terminating the tubing product, providing for each of the central passage of the tubing and the lumen of the support bead to be connected to respective fittings in fluid flow relation.
These and other objects are achieved by the present invention which provides apparatus for combining a thin film or ribbon, and a supporting bead defining one lumen or plural lumens to make a flexible tubing, and provides a method for producing the tubing in a single winding and bonding operation. The present invention employs a winding mechanism which accepts in sequence: an extruded plastic flat ribbon, and one or plural extruded supporting bead(s). The ribbon is helically wrapped so that its edges overlap and simultaneously heat-bond to themselves to form a lap joint. A bead is laid atop the ribbon and heat-bonded to the ribbon at the lap joint, forming a unitary body as described below. If plural beads are used each in turn is wound around the tube parallel with the first in similar fashion. One or more of the beads defines a single or plural lumens extending helically along the tubing product. Each lumen inside the bead will retain the same approximate size and shape free from obstruction for the entire length of the tubing product. As the bead is extruded a small amount of regulated air or gas pressure is introduced into the lumen in such a fashion as to keep the lumen open, and to insure that it retains a uniform cross sectional size and shape.
Another embodiment of the invention utilizes the tubing body construction and support bead type as described above with the added feature of having a pair of electrical conductors encapsulated within the tubing body and immediately under the support bead. One use for such electrical conductors is as an electrical resistance heating conductor to offset heat loss to ambient from warmed tidal air flow in the tube. Another use for such an electrical conductor pair would be as an electrical link between an electrical sensor and a device responsive to this sensor.
While other heat-bondable plastics may be successfully used to make the flat ribbon which becomes the wall of the present tubing product, for a variety of medical applications a polyolefin plastomer such as EXACT(trademark) is preferable. The properties of this material include chemical purity, reusability, transparency and resistance to damage from sterilization. Thermoplastic rubbers such as SANTOPRENE(trademark), or thermoplastic elastomer such as SARLINK(trademark), are suitable materials for ribbon formation, although their transparency is inferior to that of EXACT(trademark), The bead material is chosen for its ability to heat-bond with the flat ribbon, and may be of the same composition as the ribbon or of a suitable compatible different composition including the materials just mentioned.
The method utilized in creating all embodiments of the invention are similar and each can be deduced from the following description. In this particular embodiment of the invention an electrical resistance heating conductor; which we shall heretofore refer to as wire is utilized. For heating purposes, the wire conductor is preferably a resistive metal such as nickel chromium alloy (i.e., nichrome wire).
The walls of the tubing are formed by overlapping, heat-bonding and cooling successive laps or convolutions of the flat ribbon as the ribbon is extruded onto canted and rotationally driven winding rolls. As in the Carlson ""061 patent, the wire is aligned precisely along an edge of a ribbon convolution which is sufficiently cooled to prevent the wire from cutting completely through the thin ribbon, yet still warm enough to partially embed the wire in the ribbon.
The configuration of the support bead is defined by splayed or relatively angulated surfaces on either side of and cooperatively defining a wire-receiving recess. The surfaces are spread angularly apart in order to form a smooth, crevice-free juncture as the bead heat-bonds to the film while the recess receives the wire, the bead thereby surrounding the wire and integrating the ribbon, wire and bead into a unitary structure. In operation, the ribbon which will form the wall of the tubing product is extruded and helically wound onto the winding rolls, preferably from an elevated position with respect to the rolls so that any sag caused by relatively low viscosity of the extrudate is reduced or eliminated.
After several wraps of the ribbon are wound on the rolls, an electrical conductor, which may be a resistance wire, is paid out through a wire-feeding mechanism to a draw point adjacent to a lap joint of the rotating work piece. At the point the wire is applied, the work piece surface is still warm enough to partially embed the wire. Thereafter, the supporting bead is extruded over the wire on a lap joint selected so that the bead fully encapsulates the wire that is still partially embedded in the outer wall of the rotating tubing. This construction process is accomplished in such fashion as to provide not only a uniform outer shape and size for the bead, but also an interior bore of passage of uniform shape and size, and at least one lumen or passage in the bead as well.
The unitary construction just described has a significant advantage in addition to an inherent resistance to the accumulation of soil and bacteria on its outer surface, and an inherent supportive strength (i.e., from the helical bead). Since a primary purpose of the lumen defined by and within the support bead is for transference and containment of a gaseous or fluid material, it is important that this helical lumen be both capable of containment of such material (i.e., by being essentially leak-free) and likewise be capable of allowing the material to flow unhindered through the lumen of the bead from one end of a length of the tubing product to the other. Such a unitary tubing construction also allows substantial benefit to be derived by insulating the heating wire from ambient conditions, as is additionally accomplished by the encapsulating bead.
Further applications of the present invention will be apparent to those skilled in the art from consideration of several fully detailed exemplary embodiments described and depicted herein. To aid in the explanation of the exemplary embodiments, reference will be made to the Figures of the appended sheets of drawings, which Figures will first be described briefly. That is, the advantages and features of the present invention will be better understood in view of the following description of several exemplary preferred embodiments of the invention when considered in conjunction with the accompanying drawings in which: